今天心血來潮回去看以前沒看完的Array，大數運算在暫存器有限的電腦是很重要的，而且也能練習對陣列的熟悉度

有了些心得後開始試著寫大數加法，寫了一整個晚上，終於弄出來了~~

雖然程式碼很難看，至少還能正確運算XD

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void plus(char first[], char second[]);

int main(void)
{

    char input[600], first[600], second[600], operat[5];
    char* token;
 
    while (fgets(input, 599, stdin) != NULL) 
    {
		// Split string into numbers and operator
		token = strtok(input, " ");
		strcpy(first, token);
		token = strtok(NULL, " ");
		strcpy(operat, token);
		token = strtok(NULL, "\n");
		strcpy(second, token);
		
		// Check operator
		if (operat[0] == '+')
		{
			plus(first, second);
			printf("%s\n", first);
		}
		else
		{
			printf("Unknown operator.\n");
		}
    }

    return 0;
}

void plus(char first[], char second[])
{
	int first_len = strlen(first);
	int second_len = strlen(second);
	int tobe_added = 0, length1, length2, buffer1, buffer2;
	char one[600], two[600];

	if (first_len > second_len)
	{
		length1 = first_len;
		length2 = second_len;
		strcpy(one, first);
		strcpy(two, second);
	}
	else
	{
		length1 = second_len;
		length2 = first_len;
		strcpy(one, second);
		strcpy(two, first);
	}

	for (int i = 1; i <= length1; i++)
	{
		if (length2 >= i)
		{
			buffer1 = one[length1 - i] - '0';
			buffer2 = two[length2 - i] - '0';
			buffer1 = buffer1 + buffer2 + tobe_added;
		}
		else
		{
			buffer1 = one[length1 - i] - '0';
			buffer1 = buffer1 + tobe_added;
		}

		one[length1 - i] = buffer1 % 10 + '0';
		tobe_added = buffer1 / 10;

	}

	if (tobe_added != 0)
	{
		char temp[] = {(tobe_added + '0'), '\0'};
		strcpy(first, temp);
		strcat(first, one);
	}
	else
	{
		strcpy(first, one);
	}
	
}